The present invention relates to disc brakes and more particularly to improvements in a disc brake housing used in large area contact disc brake for vehicles.
The disc brake housing of the present invention is used in disc brake assemblies of the type described in the applicant""s PCT application of PCT/CA97/01014, entitled IMPROVED DISC BRAKE ASSEMBLY and published as WO98/29671 on Jul. 9, 1998. The disc brake assembly refers to full annular disc brakes proposed for automobiles and light trucks.
The full annular disc brake assembly described in this PCT application generally includes a housing mounted to a vehicle and a rotor disc mounted to a wheel of the vehicle. First and second annular brake pads extend parallel to the rotor disc within the housing and are mounted thereto. The second brake pad is movable axially by means of a fluid bladder mounted to the housing. The fluid bladder moves the second brake pad axially against the rotor disc. When pressure is applied to the rotor disc by the second brake pad and the bladder, the rotor disc is adapted to slide axially towards the first brake pad so that the rotor disc frictionally engages the first and second brake pads.
It has been found that vibrations between the first and second brake pads and the rotor disc are the major causes for break squeal.
The analysis of a vibration response is of considerable importance in the design of brakes that may be subjected to dynamic disturbances. Under certain situations, vibrations may cause larger displacements and severe stresses in the brake. The velocity of a braking system is, in general, proportional to its frequency and hence the viscous damping force increases with the frequency of the vibration. Forces resisting a motion also arise from dry friction along a non-lubricated surface. It is usually assumed to be a force of constant magnitude but opposed to the direction of a motion. In addition to the forces of air resistance and external friction, damping forces also arise because of imperfect elasticity or internal friction, called hysteric damping, within the body. The magnitude of such force is independent of the frequency but is proportional to the amplitude of vibration or to the displacement.
In the disc brake assembly elastic rolling seals are provided between the axially slidable rotor disc and the hub adapter, and between the second slidable brake pad and its support structure. The elastic rolling seal members are deformed and store energy therein when the rotor disc and the second brake pad are moved towards the first brake pad by the fluid bladder. When the brakes are released, the elastic rolling seals will be restored because of the energy stored therein and will return to the original shape, thereby moving the rotor disc and the second brake pad away from the first brake pad to release the frictional engagement therebetween. The elastic rolling seals also serve to suspend the rotor disc and the second brake pad to absorb the vibration energy and damp the vibration of the rotor disc and the second brake pad. In order to avoid self-induced evaporation phenomenon, the opposed annular friction surfaces on the rotor disc have different radii and the first and second annular brake pads are radially staggered accordingly so that these vibrations induced therefrom are at different frequencies and thus reduce the chances of harmonics, which helps to reduce the brake squeal and stresses which might occur in the disc brake.
The disc brakes described in the applicant""s patent application PCT/CA97/01014 work well and are welcomed by customers. However, there are still needs for additional improvements to further reduce the vibrations and the brake squeal caused therefrom to a lower level.
It is an object of the present invention to provide a disc brake housing, especially for a full annular disc brake for automobiles, that has an improved configuration to aid in better reduction of vibrations and brake squeals caused from the vibrations.
It is another object of the present invention to provide a disc brake housing which is easy for assembly.
It is yet another object of the present invention to provide a disc brake shoe that has an improved configuration for attachment to a disc brake housing to aid in better reduction of vibrations.
It is a further object of the present invention to provide a disc brake assembly that is provided with improved damping means to reduce the vibrations induced from the annular brake shoes.
Generally a disc brake assembly for a vehicle wheel includes a housing, first and second annular brake shoes and a rotor disc having first and second annular radial planar surfaces substantially parallel to each other. The rotor disc is coaxially mounted to the wheel and axially movable with respect to the wheel.
The disc brake housing of the assembly comprises an annular radial wall operatively supporting the first annular brake shoe adjacent to the first friction surface of the rotor disc. The annular radial wall is axially spaced apart from and connected to an annular support radial wall, which is adapted to be mounted to a frame of the vehicle and operatively supports the second annular brake shoe adjacent to the second friction surface of the rotor disc. Means are provided for restricting the respective first and second brake shoes from rotating with the disc.
An annular fluid expandable bladder extends between the second radial wall and the second brake shoe, whereby upon expansion of the bladder the second brake shoe moves axially towards the rotor disc and further presses the rotor disc against the first brake shoe, resulting in respective frictional engagement between the first friction surface of the rotor disc and the first brake shoe, and between the second friction surface of the rotor disc and the second brake shoe.
The disc brake assembly, in accordance with one aspect of the present invention, further includes damping means between the first radial wall and the first brake shoe for damping vibration produced from the first brake shoe when the first brake shoe is frictionally engaged with the first friction surface of the rotor disc.
The damping means preferably comprises a plurality of damping pads which are preferably made of a resilient and deformable material. The damping pads are circumferentially spaced apart from one another and attached to an exterior periphery of an axial portion of the first brake shoe. The damping pads are positioned to contact the inner edge of the annular radial wall so that the first brake shoe is radially and resiliently supported by the first annular radial wall. The annular radial wall preferably includes an annular ridge raised from an inner surface of the wall to abut a radial portion of the first brake shoe when the first brake shoe is pressed by the rotor disc during the frictional engagement. Thus, the first brake shoe is axially supported by the annular radial wall through the annular ridge. However uneven or various axial forces applied to the first annular brake shoe from the rotor disc, which might result from uneven wearing, imperfect machining or other defects of the parts and generally cause the vibration of the first annular brake shoe, will cause local portions of the first annular brake shoe to oscillate about the contact point on the annular ridge of the annular radial wall. The local oscillation of the first annular brake shoe about the contact point on the annular ridge of the annular radial wall causes a radial vibration of the local axial portion of the first annular brake shoe. The radial vibration will be damped by the damping pads and will not be further transferred to the annular radial wall and other structure of the disc brake assembly.
In accordance with another aspect of the present invention, a disc brake housing for the brake assembly comprises an annular radial wall operatively supporting a first annular brake shoe adjacent to the first friction surface of the rotor disc. The annular radial wall is axially spaced apart from and connected to a radial support wall. The annular radial wall includes a plurality of axial link members circumferentially spaced apart from one another and integrally extended from the first radial wall. The annular support second radial wall is adapted to be mounted to a frame of the vehicle and operatively supporting a second annular brake shoe adjacent to the second friction surface of the rotor disc. Clip means is provided at the distal end of each of the link members to enable the link members to clip onto the external periphery of the annular support second radial wall.
The clip means preferably include a distal end edge bent at a substantially right angle with respect to the link member. The clip means further include a pair of shoulders flanking the link member and spaced apart from the bent end edge. When the clip means of each member clips on the external periphery of the annular support second radial wall, a resilient force produced by the formation of the link member enables the bent end edge and the shoulders to abut a pair of opposed radial surfaces of the annular support second radial wall to secure the radial wall therebetween.
The disc brake housing according to the present invention, further improves the disc brake assembly described in the prior art, using the damping means to resiliently support the first brake shoe on the radial wall. Now the rotor disc and the first and second brake shoes are all resiliently supported. Therefore, the vibrations from these parts will be damped and not further transferred to the housing structure, and the brake squeal is reduced to a further lower level. The disc brake housing uses a link member to connect the two opposed radial walls of the housing instead of a complete cylindrical wall used in the prior art. With such configuration, the weight of the brake assembly is reduced and therefore the cost of manufacturing the disc brake assembly is also reduced. In addition, the spaced link member structure is better than the cylindrical wall to reduce the possible vibration of the brake housing.
Other features and advantages of the disc brake housing according to the present invention will be understood with reference to the preferred embodiments described below.